IF YOU CAN SEE THIS go to /sfa/Nuprl/Shared/Xindentation_hack_doc.html
At:
append split211 1. T : Type
2. L : T List
3. P : ||L||Prop
4. x:||L||. Dec(P(x))
5. i,j:||L||. P(i) i<jP(j)
6. i : ||L||
7. P(i)
8. j:i. P(j)
L_1,L_2:T List. L = (L_1 @ L_2) & (i:||L||. P(i) ||L_1||i)